The present invention relates in general to semiconductor device manufacturing, and in particular to a method for removing photoresist from a substrate (also termed a wafer) during the fabrication of semiconductor devices.
During semiconductor device manufacturing, photoresist is uniformly coated over a semiconductor substrate and then photolithographically exposed and developed to form a mask which can be used to define features of selected elements of semiconductor devices being formed on or within the substrate. In some instances, the photoresist after inspection is found to be substandard. To salvage the semiconductor substrate for reuse, the substandard photoresist must be removed (i.e. stripped) and the substrate restored to its former condition prior to coating with the photoresist.
Photoresist stripping is generally performed using a plasma. However, plasma stripping is a lengthy process which is generally performed in a different processing bay devoted to plasma etching. As a result, the substrate must be removed from a batch of substrates being processed so that the photoresist can be plasma stripped. Further processing of the batch of substrates must be delayed pending stripping of this substrate, or alternately the stripped substrate must be inserted into another batch of substrates further behind the original batch in the semiconductor process line. Plasma stripping of photoresist is also a relatively dirty process, requiring further cleaning of the substrate with an acid or solvent. Finally, the use of energetic particles in the plasma to remove the photoresist can also be damaging to the substrate and to other layers formed on the substrate (e.g. a thin oxide layer for forming the gates of transistors).
What is needed is a process for simply, quickly and effectively removing a substandard layer of photoresist from a semiconductor substrate so that the substrate can be reworked and reunited with the remaining substrates in the batch prior to further processing of the batch. The present invention provides just such a method.
An advantage of the present invention is that a substandard layer of photoresist can be completely and cleanly removed from a semiconductor substrate in a matter of a few minutes, without the substrate ever leaving a photolithographic track used for coating, exposing, developing and inspecting substrates.
A further advantage is that the method of the present invention can be incorporated into photolithography (also termed microlithography) equipment used to coat, expose, develop and inspect a photoresist layer formed on one or more semiconductor substrates so that chemical stripping of an unwanted layer of the photoresist can be performed seamlessly and automatically.
Yet another advantage of the present invention is that one or more substrates having a substandard layer of photoresist thereon can be processed to chemically strip the unwanted photoresist at the same time that other substrates within the same batch of substrates are being coated, exposed, developed, baked or inspected, thereby minimizing any delay in processing the batch to rework the photoresist layer on one or more substrates therein.
These and other advantages of the present invention will become evident to hose skilled in the art.
The present invention relates to a method for reconditioning a surface of a semiconductor substrate (e.g. comprising silicon) to remove an unwanted layer of photoresist therefrom during semiconductor device fabrication. The method comprises dissolving the layer of photoresist by rotating the substrate and contacting the layer of photoresist on the surface of the rotating substrate with a stream of a first solvent (e.g. acetone), with the first solvent and the dissolved photoresist further being urged off the surface of the substrate by the rotation thereof; cleaning the surface of the substrate and removing any of the remaining first solvent or dissolved photoresist from the surface of the substrate by contacting the surface of the substrate with a stream of a second solvent (e.g. methanol) while the substrate is being rotated; and drying the substrate and removing any of the remaining second solvent from the surface of the substrate by rotating the substrate for a time after the streams of the first and second solvents have been shut off.
The rotation speed of the substrate can be reduced during cleaning the surface of the substrate as compared to the rotation speed used during the step for dissolving the layer of photoresist. The rotation speed can then be optionally increased to aid in during drying the substrate. The exact rotation speeds for the various process steps can be selected depending upon a particular size semiconductor substrate. As an example, a rotation speed of 3000 revolutions per minute (rpm) or higher can be used during the step for dissolving the layer of photoresist; and the rotation speed can be reduced to between 2000 and 3000 rpm during cleaning the surface of the substrate.
The stream of the first solvent contacts the photoresist for sufficient time to dissolve substantially all the photoresist for removal thereof by centrifugal force provided by the rotating substrate, with the stream of the first solvent preferably being directed proximate to the center of the surface of the substrate during the step for dissolving the photoresist. The stream of the second solvent is also initially directed proximate to the center of the surface of the substrate, and can then be moved toward the edge of the substrate during the step for cleaning the surface of the substrate. This helps to ensure that the first and second solvents and the dissolved photoresist are all swept off the surface of the substrate by the centrifugal force produced by the rotating substrate. The stream of the first solvent (e.g. acetone) is generally shut off within a few seconds after the stream of the second solvent (e.g. methanol) contacts the surface of the substrate; and drying of the substrate by evaporation of any remaining solvent occurs within 30-60 seconds after both the streams of the first and second solvents have been shut off.
The present invention further relates to a method for removing photoresist from a semiconductor substrate during semiconductor device fabrication, comprising the following steps in order: contacting a surface of the substrate containing the photoresist to be removed with a stream of acetone while the substrate is being rotated, with the stream of acetone being initially directed proximate to the center of the surface of the substrate and thereby dissolving and removing at least a portion of the photoresist; contacting the surface of the substrate with a stream of methanol while the substrate is being rotated for removing any remaining dissolved photoresist from the surface of the substrate, with the stream of methanol being initially directed proximate to the center of the surface of the substrate, and overlapping in time with the stream of acetone, and with the stream of methanol continuing to be present for a period of time after the stream of acetone is shut off; moving the stream of methanol away from the center of the surface of the substrate toward an outer edge thereof during the period of time after the stream of acetone has been shut off, and simultaneously reducing the rotation speed of the substrate; shutting off the stream of methanol proximate to the outer edge of the substrate; and drying the substrate by continuing to rotate the substrate for a time after the stream of methanol has been shut off.
The rotation speed of the substrate during the step for contacting the surface of the substrate with the stream of acetone is preferably higher than the rotation speed during the step for moving the stream of methanol away from the center of the surface of the substrate toward the outer edge thereof; and the rotation speed during the step for drying the substrate will generally be greater than or equal to the rotation speed during the step for moving the stream of methanol away from the center of the surface of the substrate toward the outer edge thereof. As examples, the rotation speed during the step for contacting the surface of the substrate with the stream of acetone can be in the range of 3000-5000 rpm; the rotation speed during the step for moving the stream of methanol away from the center of the surface of the substrate toward the outer edge thereof can be in the range of 2000-3000 rpm; and the rotation speed during the step for drying the substrate can be in the range of 2000-5000 rpm. As previously mentioned, the streams of acetone and methanol are overlapped in time for a few seconds or less; and the time for drying the substrate is generally 30 to 60 seconds.
The present invention also relates to a method for removing photoresist from a surface of a semiconductor substrate during semiconductor device fabrication which comprises rotating the substrate at a first rotation speed, and contacting the photoresist on the surface of the rotating substrate with a stream of acetone, thereby dissolving the photoresist, with the acetone and dissolved photoresist further being urged off the surface of the substrate by the rotation of the substrate; cleaning the surface of the substrate to remove any remaining acetone or dissolved photoresist from the surface of the substrate by contacting the surface of the substrate with a stream of methanol while the substrate is being rotated at a speed between the first rotation speed and a second rotation speed; and drying the substrate to remove any remaining methanol by continuing to rotate the substrate at a speed between the first and second rotation speeds for a time after the streams of acetone and methanol have been shut off.